1. Field of the Invention
The present invention relates to an oven for the vacuum brazing of a metal such as aluminum or aluminum alloys.
2. Description of the Prior Art
It is generally known that in the present state of the technique vacuum brazing of aluminum takes place in the following way:
the parts to be brazed together are disposed inside an oven having a structure similar to that of a conventional oven for the heat treatment in a vacuum of metals, said parts having at least, at the level where the brazing is to be carried out, a plating of a eutectic compound for example having an aluminum and silicon base; at the same time magnesium in the form of chips or wafers is placed in the vicinity of these parts;
then a relative vacuum is provided in the oven at a pressure of about 10.sup.-4 to 5.times.10.sup.6 mbar;
then the oven is heated until the brazing temperature (between 500.degree. C. and 600.degree. C.) is obtained.
During this heating, an oxygen absorption effect is first of all obtained by oxidization (combustion) of the magnesium (Getter effect) which starts at a temperature of about 350.degree. C. Such absorption of the oxygen results more particularly in preventing the formation of alumina on the parts to be treated and more particularly at the level where the brazing is to take place. This reaction also causes elimination of the water vapor (reduction of the water).
This technique, although giving good results, nevertheless has drawbacks mainly due:
to an intense formation of magnesium oxide not only at the surface of the magnesium but also throughout the inner volume of the oven (because of the evaporation of the magnesium); the result is pollution of the oven by the magnesium oxide which will further have a tendency to absorb the humidity of the air during the opening phases of the oven, this latter will then have to be frequently cleaned;
to humidity; in fact, the presence of water vapor inside the oven and particular that due to the hygrometry of the magnesium oxide results in a poor operation of the usual vacuum pumps which usually use the diffusion of oil vapor, and it will take longer to reach the treatment pressure, with an increased energy consumption;
to an excessive consumption of magnesium which is a relatively expensive metal.
The invention proposes then overcoming these drawbacks.